1. Field of the Invention
The present invention relates to an ink jet recording method and apparatus, which comprises a plurality of recording heads each having a plurality of ejection orifices, and performs recording by ejecting an ink to a recording medium, and, more particularly, to an ink jet recording method and apparatus for recording thinned recording data.
2. Related Background Art
In recent years, OA equipments such as computers, wordprocessors, copying machines, and the like have come into general use, and many recording systems for recording apparatuses for these OA equipments have been developed. An ink jet recording apparatus has excellent features. That is, the ink jet recording apparatus allows easy high-resolution recording, and has a high-speed, low-noise, and low-cost structure. In order to meet needs for color recording, many color ink jet recording apparatuses have also been developed.
An ink jet recording apparatus ejects an ink from nozzles to cause the ink to be attached to a recording paper sheet, thereby forming an image. Conventionally, in order to improve the gradation characteristics of a recorded image, and to increase the density of the image, a plurality of pixels that form an image on a recording medium are formed by a plurality of overlapping ink droplets. In order to increase the density of adjacent pixels, a plurality of ink droplets are implanted at a high density. Upon application of these techniques to color recording, color reproducibility can be improved. Furthermore, when the recording medium is, e.g., a transparent film for a transmission type OHP (overhead projector), the transmission density of an image recorded on such a transparent film must be entirely increased. In this case, the above-mentioned techniques are effective.
In a color ink jet recording apparatus, color mixing (boundary blur) occurs at a boundary portion between a given color and another color due to diffusion of dyes, resulting in deteriorated quality of an image. The boundary blur occurs in such a manner that when an ejected ink dot, which is not sufficiently dried and fixed, is present on and in a sheet surface, it is mixed with another adjacent color ink dot. In other words, the boundary blur occurs since dyestuffs (colorants such as dyes, pigments, or the like) are diffused at a liquid-liquid interface between different inks.
In a recording medium such as an OHP film having a limited ink reception quantity, or a recording medium having poor ink absorbency, the ink absorption quantity or speed is limited, and the ink overflows from a pixel, resulting in deteriorated quality of an image. In particular, since a plurality of recording heads corresponding to ink colors are arranged in a scan direction, when different inks are implanted to overlap each other, the implantation density per unit time is increased, and the problem of ink overflow is outstanding. A color ink jet recording apparatus normally forms intermediate colors by properly overlapping cyan, magenta, and yellow color ink dots. More specifically, red can be realized by overlapping magenta and yellow ink dots; blue can be realized by overlapping cyan and magenta ink dots; and green can be realized by overlapping cyan and yellow ink dots. Note that black can be realized by overlapping three colors, i.e., cyan, magenta, and yellow. At this time, only black is separately implanted (using a black ink) due to poor color development of black and an increase in ink implantation quantity per unit area upon overlapping of inks of three colors. Therefore, since each of red, blue, and green portions where inks of two colors are implanted for each ink dot particularly has a high ink printing density per unit time, the above-mentioned ink overflow easily occurs, and boundary blur easily occurs at a boundary portion between these colors and another adjacent color.
A recording paper sheet (coated paper sheet) having a specially increased ink absorption quantity is known. However, when an ink jet recording apparatus is arranged for only such special-purpose paper sheets, a user cannot use other types of paper, and paper sheets becomes very expensive. When a user uses another type of paper or recording medium having poor absorbency, a recording error occurs. In the worst case, the user may erroneously judge that a recording head is defective, and may waste the recording head.
In recent years, with the advent of low-cost recording apparatuses, the demand for recording apparatuses that can perform recording on normal paper (e.g., PPC paper) having no special coating for improving ink absorbency has increased. However, a recording paper sheet having poor ink absorbency not only easily causes boundary blur at a boundary portion between different colors but also has a low print density as compared to an ink jet special-purpose paper sheet, which is manufactured in consideration of ink absorbency. In a recorded image, an importance is placed especially on the density of black used for characters and thin lines.
In the conventional method, in order to prevent boundary blur caused by ink overflow, a multi-pass print method is proposed. In this method, the number of ink droplets to be implanted in a single scan operation of each recording head is thinned out at the same ratio to decrease the total quantity of ink droplets to be implanted in the single scan operation, and a plurality of number of times of scan operations are performed at predetermined time intervals. In order to increase the density of black for characters and thin lines, a combined method of the multi-pass print method and a method of implanting only a black ink dot twice at the same position is also proposed.
However, in this method, the number of times of scan operations is doubled since black ink is implanted twice at the same positions for black dots, thus considerably decreasing the recording speed.